1. Field of the Invention
The present invention relates to a recording sheet for use in an ink jet recording process. More specifically, the present invention relates to an improved transparency recording sheet.
2. Description of the Prior Art
Ink jet printing refers to a method of forming type characters on a substrate, e.g., paper, by ejecting ink droplets from a printhead having one or more nozzles. Several schemes are utilized to control the deposition of the ink droplets on the printing substrate or recording sheet to form the desired characters. For example, one method comprises deflecting electrically-charged droplets by electrostatic means. Another method comprises the ejection of single droplets under the control of a piezoelectric device. One type of ink employed is the so-called non-drying type which functions by quickly penetrating the substrate, e.g., paper fibers, thus giving the appearance of being dry to the touch even though still possessing a quantity of relatively low vapor pressure solvent. Another widely used type of ink is the aqueous ink, that is, an ink which is composed of a relatively large quantity of water which functions as the solvent and carrier for the dyes therein.
The image generated by an ink jet printing device may be either in the form of a reflection print wherein the image is deposited on a substantially opaque reflective substrate, e.g., paper, or may comprise a transparency, that is, when the image is formed on a substantially transparent recording substrate and is viewed by illuminating the side of the substrate opposite the image side and viewing from the image side. Such material is, of course, particularly advantageous for use in viewing by projection.
Since projection of a transparency generally involves enlarging of the image, the image quality requirements are more stringent for a transparency than for an image viewed by reflection. Of course a transparency must take into consideration the other problems which may be common to both the transparency and to the reflection image, for example, the water fastness problem of aqueous inks. Moreover, the use of ink jet printing for achieving high speed recording on plastic transparencies has been largely unsuccessful due to the transparent polyester film support repelling the aqueous-miscible ink solutions. As well, the ink tends to coalesce on itself creating unwanted voids on the transparency.
Thus, problems exist in the use of transparencies as to the density of the images, the smear resistance of the ink, as well as an even surface distribution of ink on the transparency so that voids and pin holes do not occur in the ink block areas. U.S. Pat. Nos. 4,474,850; 4,503,111; 4,528,242 and 4,547,405 disclose various ink jet transparencies, some of which overcome the problems of smear resistance. However, severe problems with obtaining an even surface distribution of ink on the transparency so that voids do not occur in the solid ink areas still exist. It would be extremely beneficial to the industry if an ink jet transparency was available which overcame such a problem.
Another problem encountered with some polymer compositions or additives for promoting ink flow is the phenomena of "cracking." Although initially the ink spreads well, upon evaporation of the water from the ink receptive substrate, the substrate shrinks leaving large open cracks in the inked or imaged areas.
Accordingly, it is an object of the present invention to provide an ink jet recording transparency which promotes an even surface distribution of ink on the transparency.
It is another object of the present invention to provide an ink jet recording transparency exhibiting greatly improved wetting of ink jet ink in solid block areas.
Yet another object of the present invention is to provide an ink jet recording transparency exhibiting improved prevention of the ink from coalescing onto itself.
Another object of the present invention is to provide an ink jet transparency which avoids the problems of "cracking."
Still another object of the present invention is to provide an ink jet recording transparency comprising a novel coating layer on the transparent substrate.
These and other objects of the present invention, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the claims appended hereto.